How severe is CVE-2021-26556?

CVE-2021-26556 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-26556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26556?

CVE-2021-26556 primarily affects Octopus Octopus Deploy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-26556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-26556 published?

CVE-2021-26556 was published on 2021-10-07 and last updated on 2026-06-17.

CVE-2021-26556

CVE-2021-26556 is a high-severity vulnerability in Octopus Octopus Deploy with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-426.

Key facts

Severity: High (CVSS 3.x base score 7.8)
CVSS v2: 4.4
EPSS exploit prediction: 0% (17th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-426
Affected product: Octopus Octopus Deploy
Published: 2021-10-07
Last modified: 2026-06-17

Description

When Octopus Server is installed using a custom folder location, folder ACLs are not set correctly and could lead to an unprivileged user using DLL side-loading to gain privileged access.

Frequently asked questions

What is CVE-2021-26556?: When Octopus Server is installed using a custom folder location, folder ACLs are not set correctly and could lead to an unprivileged user using DLL side-loading to gain privileged access.
How severe is CVE-2021-26556?: CVE-2021-26556 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-26556 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26556?: CVE-2021-26556 primarily affects Octopus Octopus Deploy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-26556?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-26556 published?: CVE-2021-26556 was published on 2021-10-07 and last updated on 2026-06-17.

References

https://advisories.octopus.com/adv/2021-01---Local-privilege-escalation-in-Octopus-Server-%28CVE-2021-26556%29.1733296189.html

Affected products (2)

cpe:2.3:a:octopus:octopus_deploy:*:*:*:*:*:*:*:*
cpe:2.3:a:octopus:octopus_server:*:*:*:*:*:*:*:*

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